1. Field of the Invention
The present invention relates to a rotary electrical machine.
2. Description of the Related Art
In a typical rail vehicle, a rotary electrical machine is mounted on a chassis suspended below the vehicle body and the vehicle is driven by transmission of the turning effort of this rotary electrical machine to the vehicle wheels through a coupling and gearwheel device.
A totally enclosed rotary electrical machine constituting an example of a prior art rotary electrical machine is described below with reference to the drawings. FIG. 1 is a cross-sectional view of such a prior art totally enclosed rotary electrical machine.
In this specification, the longitudinal direction of the rotor shaft is defined as the axial direction.
The arrows in the Figure indicate the direction of air flow.
In the prior art totally enclosed rotary electrical machine shown in FIG. 1, a stator core 4 is provided that is restrained by a core support 4a and core support 4b, between a frame 1 provided on the side opposite to the drive side and an outer peripheral bracket 2a provided on the drive side. An inner peripheral bracket 2b is provided at the inner periphery of the outer peripheral bracket 2a and a housing 3 is provided at the inner periphery of the frame 1. A rotor shaft 7 is freely rotatably supported by bearings 5, 6 that are respectively mounted on the inner peripheral bracket 2b and housing 3. A rotor core 8 is provided in the central section in the axial direction of this rotor shaft 7. A drive side end 7a of this rotor shaft 7 extends outside the machine. A coupling is mounted on this extension. A first ventilation fan 9a is mounted on the rotor shaft 7 on the inside of the bearing 6 and a second ventilation fan 9b is mounted on the opposite side to the drive side of the rotor shaft 7 and on the inside of the bearing 5. Inlets 1a and outlets 1b are provided on the side faces of the frame 1 on the opposite side to the drive side. Through-flow passages are provided in the inner peripheral bracket 2b, the outer peripheral bracket 2a, stator 4 and frame 1. The inlets of the first ventilation fan 9a on the drive side of the rotary electrical machine form external air inlets.
The bearing of the totally enclosed rotary electrical machine is constituted by forming a minute gap between the side of the fixed member and the side of the rotary member; the interior of the rotary electrical machine is thus cut off from the outside i.e. the electrical machine is totally enclosed. External air flowing in from the inlets due to the rotation of the first and second ventilation fans 9a and 9b flows through a through-flow passage (not shown) in which the inner peripheral bracket 2b, outer peripheral bracket 2a, stator 4 and frame 1 are provided and flows out through outlets (not shown) of the frame 1. Due to this passage of external air therethrough, heat evolved by the stator core 13 and rotor bar 14 that is transmitted to the core 12 (not shown) and the frame 1 from the wall of this ventilation passage is removed by being discharged to the external atmosphere. Also, inflow of external air from the inlets 1a is produced by the rotation of the second ventilation fan 9b, thereby cooling the air in the stator core 13 and rotary electrical machine transmitted to the ventilation fan 9b. 
A prior art totally enclosed rotary electrical machine constructed in this way had the advantage that there was no possibility of contamination due to deposition of dust mixed with the external air on internal portions of complex structure, since external air cannot flow into the machine, and furthermore had the advantage that a filter to remove dust was unnecessary, since there was no possibility of dust from the external air being deposited, because the cooling effected by the external air took place by passage of the external air through a ventilation passage having a simple structure.
Such a technique is to be found in Laid-open Patent Publications in Japan such as for example Japanese Laid-open Patent Publication No. 2003-18795.
However, in this prior art rotary electrical machine, the temperature of the bearings and of the grease used to lubricate these becomes high, and this made it necessary to carry out maintenance of the bearings at short intervals.